Crystal oscillators and crystal-oscillator systems are used to provide a precision time reference for many applications, such as processing and computing systems including communication devices. Some conventional crystal-oscillator systems employ large resistors and/or capacitors for low-pass filtering as part of a feedback process to limit the amplitude of the oscillation frequency. One problem with these conventional crystal-oscillator systems is that the large resistors and capacitors usually require a large amount of circuit area on a die. Another problem with these large resistors and capacitors is that they are susceptible to process variations making it difficult to design and fabricate accurate oscillator circuits. Another problem with these conventional crystal-oscillator systems is that their output level may vary over time due to environmental factors.
Thus, there are needs for improved oscillators and methods.